Group function processing of NULL values

Group function processing of NULL values Group functions ignore null values in the column (GROUP functions ignore NULL values) as follows: SQL> select count (*) from employees; COUNT (*) ---------- 107 SQL> select count (commission_pct) from employees; COUNT (COMMISSION_PCT) ------------------- 35 has 107 rows in the employees table, but the commission_pct column with non-null values has only 35 rows. SQL> select avg (commission_pct) from employees; AVG (COMMISSION_PCT )-------------------. 222857143 SQL> select avg (nvl (commission_pct, 0) from employees; AVG (NVL (COMMISSION_PCT, 0 ))--------------------------. 072897196 by comparing the results of the two average values, we can see that during group function calculation, the null value is discarded. Note: you cannot use group function in the where clause because the where clause is executed first.